cmd/gomobile: remove an unsed function

Change-Id: I2d5fcebd96de1d81d01c2b0765a292897b404a5a
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/208058
Run-TryBot: Hajime Hoshi <hajimehoshi@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/cmd/gomobile/build.go b/cmd/gomobile/build.go
index 9a980ff..449dc9f 100644
--- a/cmd/gomobile/build.go
+++ b/cmd/gomobile/build.go
@@ -194,16 +194,6 @@
 	return nmpkgs, nil
 }
 
-func importsApp(pkg *build.Package) error {
-	// Building a program, make sure it is appropriate for mobile.
-	for _, path := range pkg.Imports {
-		if path == "golang.org/x/mobile/app" {
-			return nil
-		}
-	}
-	return fmt.Errorf(`%s does not import "golang.org/x/mobile/app"`, pkg.ImportPath)
-}
-
 var xout io.Writer = os.Stderr
 
 func printcmd(format string, args ...interface{}) {